It is known that top materials such as fabric, leather, a film, or the like, can be underlaid with plastic so that a double layer molded part of a composite material results. Such composite molded parts have manifold applications, for example in the automobile industry as inside door linings, roof linings, auto seat parts, or the like.
Underlaying with plastic has the advantage that the flexible top material is solidly joined to a form-stable support material, so that it can easily be fastened to a substructure. Separate stretching and gluing of the top material to a support material is thus obviated. Underlaid composite parts thus make possible rapid, simple, economical, and qualitatively high grade production. Furthermore, no adhesive needs to be used, so that unpleasant, often hazardous vapors also are avoided.
When underlaying the often sensitive top materials, care must be taken not to damage them. For this purpose, the plastic is injected at the lowest possible pressure into the mold cavity, in which the top material is already situated. The injected plastic here presses the top material against the cavity wall. Injecting at a low pressure is made possible in that the injection molding tool at first is not completely closed, but remains slightly open, for example, 2 to 10 mm. To prevent plastic injected in this position from exiting beyond the edge of the cavity, known injection molding tools have a female mold plate with a so-called dipping edge, i.e., an extension of that wall of the female form plate which bounds the cavity. In known injection molding tools, this dipping edge is a fixed part of the female mold plate. Together with an oppositely situated dipping edge of the mold core, it forms a dipping edge gap, which can be slightly tapered, for example, at an angle of 5xc2x0. The top material, which has been inserted into the cavity before the underlaying process, also extends into the dipping edge gap. When the injection molding tool is completely closed, which is done while the plastic is being injected, it is clamped into the dipping edge gap.
A disadvantage of the known apparatuses is that, when the dipping edge of the female mold wears outxe2x80x94and it wears out considerably due to the relatively high stressxe2x80x94the entire female mold plate must be replaced or refurbished. Furthermore, it is not possible to change the size of the dipping edge gap, which would be desirable for various reasons, for example for different top materials.
Thus, an injection molding apparatus is provided which makes it possible to underlay top material with minimal apparative and operational complexity, and which can operate in a qualitatively especially high grade manner.
In one embodiment of the inventive injection molding apparatus, the dipping edge of the female mold is formed at a dipping edge slider which is movably mounted on the female mold plate.
The inventive dipping edge slider has the advantage that it can be replaced when it wears out, without needing to replace the entire female mold plate or having to refurbish the contour regions of the cavity. This saves considerable costs and time. Furthermore, by appropriately positioning the dipping edge slider, it is possible to change the size of the dipping edge gap and to adjust it optimally for the top material. In this way, the measure by which the top material is pressed together when the injection molding tool is completely closed can be finely regulated. Distortion and ugly markings caused by over stretching the top material likewise can be avoided, since the dipping edge gap can be enlarged somewhat as necessary. Furthermore, it is possible to adjust the dipping edge slider in such a way that, when the injection molding tool is completely closed, a very slight amount of plastic can still exit from the cavity into the dipping edge gap. This creates a stiff separation point, which later makes it possible to separate the top material easily at this point.
According to an advantageous modification, the dipping edge on the mold core side is formed on a separation slider that is movably guided in the mold core. The sides with the dipping edge gap can also be appropriately adjusted and changed by means of such a separation slider. Appropriate gap dimension adjustment elements can be used for this purpose as may be necessary. Furthermore, the separate separation slider has the advantage that it can be replaced in case of wear, without needing to replace or refurbish the above mold core plate or the mold core.
It is especially advantageous for the separation slider to have a cutting edge to cut off the top material at the end of the cavity. With this modification, the separation slider, which bounds the dipping edge gap, is simultaneously used to cut off the top material at the end of the cavity after the underlaying process. During the injection molding process, the separation slider functions to bound the cavity along its edge, so as to prevent the plastic from undesirably exiting there. The separation slider can be moved, so as to accomplish the cutting process, while the injection molding tool is closed, immediately after the injection process, as soon as the plastic has appropriately solidified. Thus, it is no longer necessary to cut off the excess top material at the edge by a separate cutting process. This results in a considerable saving of time. Furthermore, it also is not necessary to provide separate cutting devices. Also, the cutting process does not involve any risk that other gated parts, for example, rubber sealing lips, are damaged.
A supplementary cavity advantageously is formed at that side of the separation slider which faces the cavity. This can be displaced by moving the separation slider between a position offset relative to the cavity and one which joins with the cavity. This supplementary cavity can be used for gating another part, for example, a rubber sealing lip, to the underlaid molded part. This gating process suitably occurs after the underlaying process in the cavity, as soon as the plastic has solidified far enough so that the separation slider, which bounds the cavity at its edge, can be moved. The gated part in this way is joined solidly to the underlaid plastic. In this way, subsequent melting of the part is obviated. A special advantage here is that two working steps can be performed by means of a single stroke motion, namely the cutting of the top material and the opening of the supplementary cavity for gating another part. The cycle time is correspondingly reduced.
According to an advantageous design, the dipping edge slider is pretensioned in its stop position by a spring force or pneumatically. When the separation slider is pulled back, the top material therefore is at first clamped in more strongly, until the spring force of the dipping edge slider has been overcome. This clamping process fixes the top material perfectly, which aids a clean and defined cut.